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BRCA1/BARD1 ubiquitinates PCNA in unperturbed conditions to promote continuous DNA synthesis.

ABSTRACT: Deficiencies in the BRCA1 tumor suppressor gene are the main cause of hereditary breast and ovarian cancer. BRCA1 is involved in the Homologous Recombination DNA repair pathway, and, together with BARD1, forms a heterodimer with ubiquitin E3 activity. The relevance of the BRCA1/BARD1 ubiquitin E3 activity for tumor suppression and DNA repair remains controversial and most efforts aimed to identify BRCA1/BARD1 ubiquitination substrates rely on indirect evidence. Here, we observed that the BRCA1/BARD1 ubiquitin E3 activity was not required for Homologous Recombination or resistance to Olaparib. Using TULIP2 methodology, which enables the direct identification of E3-specific ubiquitination substrates, we identified substrates for BRCA1/BARD1. PCNA is ubiquitinated by BRCA1/BARD1 in unperturbed conditions independently of RAD18, avoiding the formation of ssDNA gaps during DNA replication and promoting replication fork stability upon replication stress, solving the controversy about the function of BRCA1/BARD1 E3 activity in Homologous Recombination.

INSTRUMENT(S): Orbitrap Exploris 480, Q Exactive

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Román González-Prieto

LAB HEAD: Román González-Prieto

PROVIDER: PXD039167 | Pride | 2024-05-07

REPOSITORIES: Pride

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Project description:Ubiquitination has crucial roles in many cellular processes and dysregulation of ubiquitin machinery enzymes can result in various forms of pathogenesis. Cells only have a limited set of E2 ubiquitin-conjugating enzymes to support the ubiquitination of many cellular targets. As individual E2 enzymes have many different substrates and interactions between E2 enzymes and their substrates can be transient, it is challenging to define all in vivo substrates of an individual E2 and the cellular processes it affects. Particularly challenging in this respect is UBE2D3, a very promiscuous E2 enzyme that affects a broad range of processes. Here, we set out to identify in vivo targets of UBE2D3 by using SILAC-based quantitative ubiquitin diGly proteomics to study global proteome and ubiquitinome changes associated with UBE2D3 depletion. UBE2D3 depletion changed the global proteome, with proteins from metabolic pathways, in particular retinol metabolism, being the most affected. However, the impact of UBE2D3 depletion on the ubiquitinome was much more prominent and, interestingly, identified pathways related to mRNA translation as top pathways being affected. Indeed, we find that ubiquitination of the ribosomal proteins RPS10 and RPS20, critical for ribosome-associated protein quality control (RQC), is dependent on UBE2D3. Moreover, we find that UBE2D3 limits monoubiquitination of histone H2B at lysine 120, mediated by the E3 ligase RNF20. This identifies UBE2D3 as a potential regulator of the diverse and critical cellular processes that are controlled by H2B monoubiquitination. Collectively, our findings show that depletion of an E2 ubiquitin-conjugating enzyme in combination with quantitative diGly-based ubiquitinome profiling is a powerful tool to identify new in vivo E2 substrates, as we have done here for UBE2D3. Together with our identification of RQC factors and H2B as novel in vivo targets of UBE2D3, our work provides an important resource for further studies on the in vivo functions of UBE2D3.

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BRCA1/BARD1 ubiquitinates PCNA in unperturbed conditions to promote continuous DNA synthesis.

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